1. Technical Field
The present invention relates to a vehicle hood, such as an automobile hood. More specifically, the present invention relates to a vehicle hood excellent in collision resistance performance with respect to the head of a pedestrian at front surface collision.
2. Description of the Related Art
In an automobile having a hood in the front portion of a vehicle body, the automobile hood has an outer panel, an inner panel, and other reinforcing members. To ensure the rigidity and strength of the hood itself, typically, the outer panel is joined to the inner panel to take a closed cross-sectional structure which closes the space therebetween.
At present, to evaluate the pedestrian protection performance at front surface collision, a Head Injury Criterion (HIC) value (head injury value) calculated from the “acceleration-time” waveform at collision is typically used. As the HIC value becomes lower, the head of a pedestrian is unlikely to be injured at collision. Therefore, a hood structure which lowers the HIC value after ensuring the dent resistance, the tensile rigidity, and the rigidity and strength of the hood is desired.
It is assumed that the head of a pedestrian collides with the center portion of the hood in a collision accident. In the acceleration waveform applied to the head, typically, a first wave occurs when the head comes into contact with the hood at the initial stage of collision, and then, a second wave occurs when the hood is moved in the vehicle downward direction and comes into contact with the hood incorporated components arranged below the hood. To reduce the HIC value, in particular, it is effective to make the second wave of acceleration smaller. For this, at head collision, it is best to absorb the collision energy before the hood comes into contact with the incorporated components. It is desirable to sufficiently ensure the gap between the hood panel and the incorporated components below the hood.
However, when considering the arrangement of the components necessary for an automobile, it is often difficult to sufficiently ensure the gap between the hood panel and the incorporated components. Therefore, desired is a hood structure in which the first wave of acceleration at head collision is increased to a maximum extent to increase the energy absorption amount at the initial stage of collision, whereby reducing the deformation stroke or bringing the second wave of acceleration smaller when the hood comes into contact with the incorporated components.
To ensure the pedestrian protection performance, a structure in which a plurality of substantially hat-shaped beads arranged in substantially parallel are formed in the center portion of the inner panel of the hood has been proposed (JP 2001-151159 A, JP 2003-205866 A, and JP 2008-30574 A). This can ensure the dent resistance and the tensile rigidity required for the hood, thereby improving the pedestrian protection performance at front surface collision.
In the feature of the inner panel of the hood, the substantially hat-shaped beads are arranged. With this, the bending rigidity of the hood panel can be increased to prevent local bending deformation at collision with the head of a pedestrian, so that the impact load can be distributed. Thus, the region in which the collided hood is shifted at head collision is large to increase its weight. As compared with the case of not providing the beads, the first wave of acceleration at head collision becomes larger. In addition, the hat-shaped beads are arranged in substantially parallel. Thus, the inner panel is likely to be deformed when it comes into contact with the incorporated components below the hood, which can make the second wave of acceleration smaller.